linux-kernel - Re: [PATCH v4 01/10] pagemap: Introduce ->memory

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Message-ID: <CAPcyv4ibuHeQ7o=sTZpQoryv=_3WuBFJhodBnAEVRPmvo=nAeQ@mail.gmail.com>
Date:   Tue, 15 Jun 2021 17:18:18 -0700
From:   Dan Williams <dan.j.williams@...el.com>
To:     Shiyang Ruan <ruansy.fnst@...itsu.com>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-xfs <linux-xfs@...r.kernel.org>,
        linux-nvdimm <linux-nvdimm@...ts.01.org>,
        Linux MM <linux-mm@...ck.org>,
        linux-fsdevel <linux-fsdevel@...r.kernel.org>,
        device-mapper development <dm-devel@...hat.com>,
        "Darrick J. Wong" <darrick.wong@...cle.com>,
        david <david@...morbit.com>, Christoph Hellwig <hch@....de>,
        Alasdair Kergon <agk@...hat.com>,
        Mike Snitzer <snitzer@...hat.com>,
        Goldwyn Rodrigues <rgoldwyn@...e.de>
Subject: Re: [PATCH v4 01/10] pagemap: Introduce ->memory_failure()

On Thu, Jun 3, 2021 at 6:19 PM Shiyang Ruan <ruansy.fnst@...itsu.com> wrote:

Hi Ruan, apologies for the delays circling back to this.

>
> When memory-failure occurs, we call this function which is implemented
> by each kind of devices.  For the fsdax case, pmem device driver
> implements it.  Pmem device driver will find out the filesystem in which
> the corrupted page located in.  And finally call filesystem handler to
> deal with this error.
>
> The filesystem will try to recover the corrupted data if possiable.
>

Let's move this change to the patch that needs it, this patch does not
do anything on its own.

> Signed-off-by: Shiyang Ruan <ruansy.fnst@...itsu.com>
> ---
>  include/linux/memremap.h | 8 ++++++++
>  1 file changed, 8 insertions(+)
>
> diff --git a/include/linux/memremap.h b/include/linux/memremap.h
> index 45a79da89c5f..473fe18c516a 100644
> --- a/include/linux/memremap.h
> +++ b/include/linux/memremap.h
> @@ -87,6 +87,14 @@ struct dev_pagemap_ops {
>          * the page back to a CPU accessible page.
>          */
>         vm_fault_t (*migrate_to_ram)(struct vm_fault *vmf);
> +
> +       /*
> +        * Handle the memory failure happens on one page.  Notify the processes
> +        * who are using this page, and try to recover the data on this page
> +        * if necessary.
> +        */

I thought we discussed that this needed to be range based here:

https://lore.kernel.org/r/CAPcyv4jhUU3NVD8HLZnJzir+SugB6LnnrgJZ-jP45BZrbJ1dJQ@mail.gmail.com

...but also incorporate Christoph's feedback to not use notifiers.

> +       int (*memory_failure)(struct dev_pagemap *pgmap, unsigned long pfn,
> +                             int flags);

Change this callback to

int (*notify_memory_failure)(struct dev_pagemap *pgmap, unsigned long
pfn, unsigned long nr_pfns)

...to pass a range and to clarify that this callback is for
memory_failure() to notify the pgmap, the pgmap notifies the owner via
the holder callbacks.